Hospitalizations for heart disease and stroke fell by about one-third over the past decade, according to a new study of nearly 34 million Medicare recipients.

The number of Medicare patients hospitalized with heart attacks fell 38% from 1999 to 2011, while the number hospitalized with blood-clot-related strokes fell 34%, according to a study in Circulation. Hospitalizations fell 31% for heart failure, which occurs when the heart is too weak to pump efficiently, and 84% for unstable angina, a sudden chest pain that often leads to heart attacks, partly because some of these cases were reclassified as heart attacks.

Fewer people died after leaving the hospital, as well.

The risk of dying within a year of being hospitalized fell 13% for patients suffering from heart failure and stroke, 21% for those with unstable angina and 23% for heart attacks.

"I don't think anyone would have predicted we would have made this much progress," says lead author Harlan Krumholz, director of the Yale-New Haven Hospital Center for Outcomes Research and Evaluation in Connecticut. "We've saved lives, we've saved suffering, we've saved dollars. It's amazing. ... What is surprising to me is how rapid and how profound the change has been."

Doctors can't point to any single big breakthrough to explain the improvements, Krumholz says.

"There was no new blockbuster drug and there was no vaccine against heart disease," Krumholz says. Yet "this is not happening by accident. A lot of people and organizations have been working really hard for the past 10 to 15 years to make better use of the knowledge we have."

Doctors, hospitals and health groups around the country focused on doing a better job of consistently getting the best care to the most people, as quickly as possible, Krumholz says. Doctors did a better job identifying and treating high blood pressure, for example, and in getting fast, appropriate treatment to heart attack sufferers.

Americans are also doing more to prevent heart disease. More adults are taking cholesterol-lowering statins and fewer are smoking, Krumholz says. The smoking rate among adults fell from 23.5% in 1999 to 19% in 2011, according to the Centers for Disease Control and Prevention.

"It's great news for patients and doctors, because it suggests that the things we've been doing for patients over the last few years have really worked," says Howard Herrmann, director of interventional cardiology and cardiac catheterization at the Hospital of the University of Pennsylvania.

Herrmann notes that the country needs to continue making progress. Heart disease remains the country's leading cause of death, with 596,577 deaths in 2013, according to the CDC.

And poor health in Americans under 65 — who are too young to receive Medicare — could reverse these positive trends, says Suzanne Steinbaum, director of women's heart health at the Heart and Vascular Institute at New York's Lenox Hill Hospital. She's particularly concerned about growing rates of obesity and diabetes and notes that heart attack rates are increasing in younger women, especially African Americans.

Although the study shows that "we can change outcomes for patients with cardiovascular disease," Steinbaum says, "we have to start with our youth."